<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>

    <style>
        *{
            margin: 0;
        }
        .left_menu{
            width: 20%;
            height: 500px;
            background-color: wheat;
            float: left;
        }
        .content_menu{
            width: 80%;
            height: 500px;
            background-color: darkgray;
            float: left;

        }

        .title{
            text-align: center;
            background-color: brown;
            line-height: 30px;
            color: white;
        }
        .item{
            margin: 20px;
        }
        .hide{
            display: none;
        }
    </style>
    <script type="text/javascript" src="jquery-3.1.1.js"></script>
</head>
<body>


<div class="outer">
    <div class="left_menu">

           <div class="item">
                <div class="title">菜单一</div>
                <div class="con">
                    <p>11111</p>
                    <p>11111</p>
                    <p>11111</p>
                </div>
           </div>

           <div class="item">
                <div class="title">菜单二</div>
                <div class="con hide">
                    <p>22222</p>
                    <p>22222</p>
                    <p>22222</p>
                </div>
        </div>

           <div class="item">
                <div class="title ">菜单三</div>
                <div class="con hide">
                    <p>33333</p>
                    <p>33333</p>
                    <p>33333</p>
                </div>
            </div>


    </div>
    <div class="content_menu"></div>
</div>
<script type="text/javascript">
    $('.title').click(function(event) {
        $(this).next().removeClass('hide').parent().siblings().children('.con').addClass('hide');
    });
</script>
</body>
</html>